This invention relates to cordless extension telephone systems and more particularly, to such systems employing a digital encoding technique to achieve access security from other systems and extraneous noise.
One of the problems with the cordless extension telephones which are presently on the market is their lack of reliable access security; that is, the systems presently in use fail to reject remote signals from other phone systems or other extraneous noise signals. Most cordless extension phone systems now in use employ a background pilot tone beyond the audible pass band. By using different pilot tones for different extension phone sets, each extension phone set is intended to exclude the signals from other sets and also from extraneous noise systems. However, the number of available security pilot tones is limited, and, with the increasing popularity of cordless extension phones and the increased proliferation of these devices over the next few years, the problem of access security on each extension phone set will become increasingly acute.
There have been proposed systems in which encoding techniques are used to achieve access security, but these systems in the prior art are relatively complex and of questionable reliability and accordingly have had no impact upon the art.